The discs of such a braking system typically are immersed in oil, and the actuator is typically hydraulically powered. The hydraulic fluid which moves the brake applying member is typically supplied by a master valve, commonly referred to as a master cylinder, which includes a piston assembly which is manually moveable, e.g. by a brake pedal, to provide pressurized hydraulic fluid to the brake actuator along a hydraulic fluid line between the master valve and a brake actuator assembly which includes the brake applying member.
Particularly but not exclusively in a “wet disc” brake system, it will be appreciated that a running clearance must be provided between the discs moved by the actuator and the discs of the member to be braked, to prevent uneven wear and/or to reduce parasitic losses resulting from churning of oil between the discs when the brake is not applied. These parasitic drag losses increase exponentially as the relative rotational speed between the discs moved by the brake actuator and the discs of the member to be braked, increases.
However, as more running clearance is provided between the respective discs when the brake is not applied, it will be appreciated that more hydraulic fluid will be required from the master valve to apply the brake, thus requiring greater movements of the foot pedal or other manual brake operating member. Large such manual movements are undesirable.
Large running clearances are really only required at high relative rotational speeds between the discs of the brake applying member and the discs of the member to be braked, i.e. in the case of an earthmoving or load handling machine, at high travelling speeds, e.g. when the machine is being driven in its highest gear at full throttle.